Current limiting device



NOV. 29, 1966 BODENSCHATZ 3,289,042

CURRENT LIMITING DEVICE Filed Jan. 24, 1963 2 Sheets-Sheet 1 INVENTOR.

406057 EODE/VJTH/ITZ g fi-rrleus/vz, F4854, 45x5; in FA? 1966 A. BODENSCHATZ CURRENT LIMITING DEVICE 2 Sheets-Sheet 52 Filed Jan. 24, 1963 IN VENTOR. A0605 7' EOflE/VJ' 619/4 72' United States Patent 3,289,042 CURRENT LIMITING DEVICE August Bodenschatz, Philadelphia, Pa, assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed .Ian. 24, 1963, Ser. No. 253,573 15 Claims. (Cl. 317-41) My invention relates to a current limiting device, and more particularly to such a device which is designed to operate in conjunction with a current interrupting circuit breaker responsive to the occurrence of a severe overload.

It is known to provide circuit protection by the combination of a relatively small circuit interrupter and a current limiting device; the former being operable under conditions of relatively low overload, and the latter being operable responsive to severe short circuit conditions. This arrangement advantageously provides satisfactory circuit protection without the need for a circuit interrupter of an excessively high rating.

One prior art arrangement consists of the combination of an electrically and mechanically coordinated circuit breaker and current limiting fuse, such as had been described in US. Patent No. 2,843,702 issued July 15, 1958 in the name of W. H. Edmunds, entitled Protective Device With Current Limiting Means, and assigned to the assignee of the instant application. In circuit interrupt? ers of this type, the circuit breaker operates to protect the line from overloads and relatively low short circuit current conditions as compared to the available short cir: cuit current. The current limiting fuse coordinated with the circuit breaker is so designed as to operate only when the short circuit current is to exceed some predetermined value. This fuse is characterized in operating in an extremely short time and in being current limiting. In operation, the current limiting fuse will limit the short circuit current and interrupt the circuit so that the maximum available short circuit current will never pass through the circuit interrupter. Because of this, it is possible to design the circuit breaker to have a relatively low short circuit interrupting ability with relation to the available short circuit current of the line being protected. Thus, the combination provides a relatively small unit for protecting a relatively high capacity line.

The disadvantage of the above-noted type of circuit interrupter is that when the fuse is operated it must be replaced. Further disadvantages lie in the relatively complex mechanism required in mechanic-ally coordinating the operation of the current limiting fuse and its associated circuit breaker.

Another arrangement of the prior art utilizes a solenoid plunger within the circuit breaker housing to render the circuit breaker limiting by causing an initial opening action of the contacts under high fault condition. Such arrangements are typically described in US. Patent No. 3,012,118 issued December 5, 1961, entitled Current Limiting Circuit Breaker in the name of W. H. Edmunds and assigned to the assignee of the instant invention; and my copending US. patent applications, Serial No. 806,041, filed April 13, 1959, entitled Current Limiting Circuit Breaker, now US. Patent No. 3,164,- 700; and Serial No. 43,680 filed July 18, 1960, entitled "ice Current Limiting Circuit Breaker, now US. Patent No. 3,127,488, both assigned to the assignee of the instant invention. In each of these arrangements one of the main contacts of the circuit breaker is operable through a mechanism auxiliary to the main operating mechanism to be initially moved to a disengaged position and thereafter retained in that disengaged position until the normal operating mechanism is appropriately actuated to retain the disengaged contacts in their opened position. Such systems disadvantage-ously require an integral relationship of the auxiliary mechanism to the circuit breaker operating mechanism; and the quick movement of a contact structure which is primarily constructed to serve other purposes than being initially moved to a disengaged position for current limiting action.

My invention avoids these disadvantages by providing a novel current limiting device responsive to severe short circuit conditions, which is neither interrupting nor mechanically connected to the operation of the circuit breaker. The device of my invention may either be located in an appropriate recess in the circuit breaker housing, or situated remote from the circuit breaker in its own individual housing. Briefly stated the current limiting device is series connected to the current interrupting cir cuit breaker and includes a variable impedance element. The variable impedance element is actuated responsive to a severe short condition to gradually introduce increased impedance into the line, thereby limiting the current. The operation of the current limiting device is appropriately coordinated with the circuit breaker, such that the current is limited to a safe value which may then be appropriately interrupted by the circuit breaker.

In a preferred embodiment of the instant invention, the device includes an elongated conductive member, of a high resistance material, which is coil wound to form a generally conical spring. When the spring is in its closed position, the adjacent turns are in an abutting electrical contact relationship about their peripheral region, thereby providing a comparatively short path of large cross-sectional area, and hence low resistance between the ends of the spring. Should the spring be separated so as to defeat the non-abutting relationship between adjacent coils, the electrical circuit now includes the elongated and smaller cross-sectional path about the individual turns; such pat-h effecting substantially more resistance between the spring ends, and an appreciable inductive change.

The conical spring member is wound about an actuating plunger which is contained in an electromagnetic circuit, which circuit also includes a cooperating yoke structure. A separate low impedance coil is electrically connected intermediate the actuating plunger and the multi-turn spring coil, which separate coil is also wound about the, actuating plunger. The electromagnetic circuit, spring biasing force and electrical circuit are appropriately interrelated such that when the overload current reaches a predetermined value the low impedance coil provides sufficient flux to initiate movement of the actuating plunger. As this occurs the spring coils will :be progressively separated, defeating the abutting relationship of adjacent turns. This causes the current to be diverted from the low resistance peripheral path to a longer path through the single turns. Since this longer path is through a substantially smaller cross-sectional area, it elfects the introduction of increased resistance to the circuit. The separation of the coil spring also provides an increasing number of flux generating turns about the actuating plunger, to effect an increase in the magnetic pull. Thus it is seen that a current limiting effect is provided by the gradual introduction of increased resistance and inductance into the circuit, such gradual increase advantageously preventing a sudden voltage surge.

As a further aspect of my invention calibration of the short circuit pickup point is provided by an adjustable biasing means, such as a spring, operatively connected to the plunger to cooperate with the biasing force of the spring coil.

It is therefore seen that the essence of my invention is to provide a non-interrupting current limiting device, which includes a conductive coil, wound to form a plurality of adjacent turns, which turns may be moved between an abutting and non-abutting relationship to effect a current limiting impedance variation.

Accordingly, a primary object of this invention is to provide a novel current limiting device.

A further object of this invention is to provide a novel current limiting device to provide circuit protection in conjunction with a circuit breaker, without any direct mechanical connection therebetween.

Another object of this invention is to provide a noninterrupting current limiting device which includes a coilwound conductive member having individual turns movable between an abutting and non-abutting relationship to effect an impedance variation.

An additional object of this invention is to provide such a current limiting device which further includes an electro-magnetic circuit, actuable by the flux established when the current therethrough corresponds to a predetermined severe short condition; the actuation of said electromagnetic circuit effecting movement of the individual turns between their abutting and non-abutting relationship.

Still a further object of my invention is to provide such a current limiting device which gradually introduces increased impedance into the circuit, to thereby avoid a voltage surge.

These as well as other objects of this invention will readily become apparent after reading the following descriptions of the accompanying drawings in which:

FIGURE 1 is an end view, partially in cross-section, of a current limiting device constructed in accordance with my invention, shown in its normally closed position, and schematically connected in a protective circuit arrangement with a conventional circuit breaker.

FIGURE 2 is a similar View of the current limiting device shown in FIGURE 1, upon initial actuation thereof and in the partially opened position.

FIGURE 3 is a similar view of the current limiting device of FIGURES 1 and 2, shown in the fully opened and current limiting position.

FIGURE 4 is a perspective view of a single coil turn provided to initiate actuation of the plunger.

Referring to FIGURE 1, the current limiting device of my invention, generally shown as 10, includes output terminals 12, 14 to be electrically connected to the circuit being protected. For example, lines 16 and 18 provide a series connection of the current limiting device and a conventional circuit breaker 17 between the terminus 20, 22 of the protective arrangement. This series protective arrangement is suitably interconnected along the current carrying power line.

Circuit breaker 17 may be of the general type disclosed in U.S. Patent No. 2,574,093 issued November 6, 1951, entitled Adjustable Trip in the name of William H. Edmunds and assigned to the assignee of the instant invention, or any other appropriate device responsive to a moderate overload or short circuit condition to disengage contacts 19 and 21. The circuit breaker includes a manual operating handle 26, and a trip unit 25 for the operation of the contacts 19-21 in the well known manner. Trip unit 25 is schematically shown connected to the external circuit via line 23, and to the movable contact carrying member 28 by the dotted line 27; the latter being an appropriate mechanical linkage. Stationary contact 19 is shown connected to the external circuit via line 29, thereby completing the circuit between 20-22. In operation, should a severe short circuit condition occur, the current limiting device 10 of my invention is designed to eifect a sufiicient impedance increase between terminals 12 and 14 to maintain the current within safe limits, with circuit breaker 17 then providing appropriate interruption.

In the preferred embodiment of my invention shown in FIGURES 1-3, the current limiting device 10 includes an elongated conductive member of a high resistance material, coil wound to form a generally conical spring 30. Spring 30 includes a plurality of adjacently positioned turns shown as 32-46. In the closed position, as shown in FIGURE 1, the adjacent turns 32-46 are all in an abutting relationship about their pen'pheral region to form a low resistance electrical path extending between oppositely disposed turns 32 and 46.

Coil 30 is positioned about actuating plunger 50, with the uppermost turn 46 being suitably housed in an insulated recess area 52. Actuating plunger 50 and coil 30 are centrally disposed within an electromagnetic yoke the actuating plunger being insulated therefrom by insulation pieces 55. The lowermost turn 32 of coil 30 is firmly seated in recesses 62 of yoke 60, and in electrical contact with the yoke in this region. A low impedance coil member 70 (better shown in FIGURE 4) is located in a suitable recess at the upper region of actuating plunger 50, and electrically connects actuating plunger 50 to coil spring 30 at its upper region. Although illustratively shown as a single-turn coil, member 70 may comprise a multicoil arrangement to provide suitable flux generation.

The current path through the current limiting device includes a first terminal member 12 which may be of any standard construction, and can receive any desired type of lug to which electrical connection may be made. Terminal 12 is appropriately connected to actuating plunger 50 which is formed of an electrically conductive material. Actuating plunger 50 is in electrical contact with ring 70, which n'ng electrically connects to the upper end of spring 30. The current path then proceeds through the conical coil 30, to its lowermost region contained within yoke recess 62. The circuit is completed through the lower portion of yoke 60 connected to terminal 14; the latter being constructed similar to terminal 12.

With the coil turns 32-46 in their abutting relation ship of FIGURE 1, a fairly low impedance path is provided between the opposite ends of coil 30 about the peripheral regions of adjacent turns. This condition is operatively related to the actuation of the device which is appropriately system coordinated to maintain this low impedance condition for normal current and moderate overload conditions.

The flow of current through single turn ring-like member 70 establishes a flux path as shown by dotted lines 64-66 which includes magnetic yoke 60; actuating plunger 50; and air gap 75, intermediate the top surface 54 of actuating plunger 50 and yoke 60. This magnetic flux is in a direction to urge plunger 50 upwards against the biasing effect of spring coil 30. Insulating material 56 is placed along interior surface 65 of the yoke to prevent electrical contact between the plunger 50 and yoke at such times as the plunger is moved upward to close the gap.

The current limiting device of my invention is appropriately calibrated with respect to the circuit being protected such that the flux generated by ring member responsive to a predetermined severe short condition initiates upward movement of plunger 50. Precise calibration of the short circuit pickup point of actuating plunger 59 is advantageously provided by an additional biasing member, such as spring 80.

Reference is now made to FIGURES 2 and 3, which illustrate the progressive upward movement of plunger 50 responsive to a severe short circuit condition. As plunger 50 begins to move upward, closing the air gap 75, the individual turns of coil 30 begin to separate from their abutting relationship to a non-abutting relationship. This separation first begins to occur at the lower end of the coil, and gradually proceeds upward. Accordingly, FIGURE Z, corresponding to the initial actuation of the plunger, shows only coils 32, 34 and 36 separated. Such separation gradually proceeds upward as plunger 54) is raised, until the fully opened position shown in FIGURE 3, wherein all the coils are moved to a nonabutting relationship.

As adjacent coils open, the low resistance path between their peripheral contact regions is defeated, thereby forcing the current to divert through the appreciably higher resistive path through the coil lengths. Further, as the coils are separated, an increasing number of turns are introduced into the electromagnetic flux generating circuit about plunger 50, thereby assisting in the upward movement of plunger 50. Thus, the separation of the coils serves to increase both the resistive and reactive components of the impedance between terminals 12 and 14. This increased impedance suitably limits the current in a sufficiently rapid time to prevent circuit damage, while still taking a sufficient length of time to prevent a sudden voltage surge.

FIGURE 4 shows, in perspective, a preferred form of the single turn 70. Turn 70 is preferably formed of a low resistance material, such as copper. Protrusions 72 and 74- mate with suitable configurations at the upper region of the actuating piston to maintain ring 70 in its operative position. The uppermost surface of protrusion 72 is in contact with coil end 48 to provide appropriate series contact therebetween. Insulator pieces 57 are provided intermediate acuating plunger 50, single turn 70 and coil 30 to maintain the above-described series current path between terminals 12 and 14, including single turn 70. The current path through single turn 70 is shown by arrow 76, which is in a proper direction to induce the flux field 64, 66, urging plunger 50 upward.

It is therefore seen that I have provided a simply and inexpensively constructed current limiting device which may be appropriately calibrated in conjunction with a conventional type of circuit breaker for coordinated line protection. Such a combination preferably permits the use of a relatively small circuit breaker unlit for protecting a line having short circuit capabilities in excess of the circuit breaker rating.

Although I have described a preferred embodiment of my novel invention, many variations and modifications will now become apparent to those skilled in the art, and I prefer therefore not to be bound by the specific disclosure contained herein but only by the appended claims.

1 claim:

1. A current limiting device comprising a first and second terminal; electrical circuit means forming a vari-' able impendance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; electromagnetic actuating means including an actuating plunger with said coil positioned about said actuating plunger and in magnetic flux coupling relationship therewith; said actuating plunger adapted to progressively move adjacently located ones of said turns between an abutting and non-abutting relationship about their peripheral region; said turns in their abutting relationship effecting a first impedance value between said first and second terminals; said turns in their non-abutting condition elfecting a second impedance magnitude between said first and second terminals; said electromagnetic actuating means constructed to initiate movement of said turns between their abutting and nonabutting relationship responsive to a current presented to said first and second terminals exceeding a predetermined value, with said non-abutted turns progressively contributing to the magnetic flux for movement of said actuating plunger,

2. A current limiting device comprising a first and second terminal; electrical circuit means forming a variable impedance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; first means adapted to operatively move adjacently located ones of said turns between an abutting and non-abutting relationship about their peripheral region; said turns in their abutting relationship effecting a first impedance value between said first and second terminals; said turns in their non-abutting condition effecting a second impedance magnitude between said first and second terminals; said first means constructed to initiate movement of said turns between their abutting and nona-butting relationship responsive to a current presented to said first and second terminals exceeding a predetermined value; said first means including an electromagnetic circuit; said turns being operatively included in said electromagnetic circuit to generate a magnetic flux; adjacent ones of said plurality of turns being progressively moved from said abutting to non-abutting relationship to form a gradually increasing number of series connected turns for generating said magnetic flux.

3. A current limiting device comprising a first and second terminal; electrical circuit means forming a variable impedance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; first means adapted to operatively move adj acently located ones of said turns between an abutting and non-abutting relationship about their peripheral region; said turns in their abutting relationship effecting a first impedance value between said first and second terminals; said turns in their non-abutting condition effecting a second impedance magnitude between said first and second terminals; said first means constructed to initiate movement of said turns between their abutting and nonabutting relationship responsive to a current presented to said first and second terminals exceeding a predetermined value; said first means including an electromagnetic circuit; said turns being operatively included in said electromagnetic circuit to generate a magnetic fiux; adjacent ones of said plurality of turns being progressively moved from said abutting to non-abutting relationship to form a gradually increasing number of series connected turns for generating said magnetic flux; said elongated conductive member formed of a high resistance material; said second impedance magnitude including a substantially greater resistive component than said first impedance magnitude, whereby current limiting is effected between said first and second terminals; said progressive movement of said turns effecting a gradual increase of impedance from said first impedance value to said second impedance value.

4. A current limiting device comprising a first and second terminal; electrical circuit means forming a variable impedance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; first means adapted to operatively move adjacently located ones of said turns between an abutting and non-abutting relationship about their peripheral region; said turns in their abutting relationship effecting a first impedance value between said first and second terminals; said turns in their non-abutting condition effecting a second impedance magnitude between said first and .second terminals; said first means constructed to initiate movement of said turns between their abutting and nonabutting relationship responsive to a current presented to said first and second terminals exceeding a predetermined value; said first means including an electromagnetic circuit; said turns being operatively included in said electromagnetic circuit to generate a magnetic flux; adjacent ones of said plurality of turns being progressively moved from said abutting to non-abutting relationship to form a gradually increasing number of series connected turns for generating said magnetic flux; a second conductive member series connected with said elongated conductive member between said first and second terminals; said first means including an actuating plunger; said second conductive member positioned about said actuating plunger to generate a magnetic flux through said actuating plunger; said magnetic flux tending to move said actuating plunger in a first direction; said turns operatively connected to said actuating plunger whereby movement of said actuating plunger in said first direction effects said progressive movement of said turns.

5. A current limiting device comprising a first and second terminal; electrical circuit means forming a variable impedance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; first means adapted to operatively move adjacently located ones of said turns between an abutting and nonabutting relationship about their peripheral region; said turns in their abutting relationship ellecting a first impedance value between said first and second terminals; said turns in their non-abutting condition effecting a second impedance magnitude between said first and second terminals; said first means constructed to initiate movement of said turns between their abutting and non-abutting relationship responsive to a current presented to said first and second terminals exceeding a predetermined value; said first means including an electromagnetic circuit; said turns being operatively included in said electromagnetic circuit to generate a magnetic flux; adjacent ones of said plurality of turns being progressively moved from said abutting to non-abutting relationship to form a gradually increasing number of series connected turns for generating said magnetic fiux; a second conductive member series connected with said elongated conductive member between said first and second terminals; said first means including an actuating plunger; said second conductive member positioned about said actuating plunger to generate a magnetic flux through said actuating plunger; said magnetic flux tending to move said actuating plunger in a first direction; said turns operatively connected to said actuating plunger whereby movement of said actuating plunger in said first direction eifects said progressive movement of said turns; said elongated conductive member formed of a high resistance material; said second impedance magnitude including a substantially greater resistive component than said first impedance magnitude, whereby current limiting is effected between said first and second terminals; said progressive movement of said turns effecting a gradual increase of impedance from said first impedance value to said second impedance value.

6. The current limiting device of claim 4 further including means biasing said actuating plunger against movement in said first direction; the magnetic flux produced by said second conductive member operatively related to said biasing means to initiate movement of said plunger in said first direction response to a current flow above a predetermined value.

7. The current limiting device of claim 6 including the series connected arrangement of said first terminal, said actuating plunger, said second conductive member; said elongated conductive member; electromagnetic yoke means; and said second terminal.

8. The circuit limiting device of claim 7, wherein said electromagnetic yoke means establishes a flux path in- 8 cluding said actuating plunger, and an air gap; said air gap positioned between said actuating plunger and said yoke means; movement of said actuating plunger in said first direction lessening the air gap separation between said actuating plunger and said electromagnetic yoke means. I

9. The circuit limiting device of claim 8, wherein said turns are wound about said actuating plunger; the uppermost one of said turns being electrically connected to said second conductive member at the upper region of said actuating plunger; the lowermost one of said turns being fixedly received by said yoke, and electrically connected thereto.

10. The. current limiting device of claim 9, wherein adjacent ones of said turns are of increasing diameter to form a generally conical coil; said uppermost turn having a diameter generally corresponding to the diameter of said actuating plunger; said lowermost turn having a diameter generally corresponding to the internal area of said yoke.

11. A circuit protective arrangement including the series connection of a current interrupting circuit breaker and a non-interrupting current limiting device; said current interrupting circuit breaker including an operating mechanism responsive to overload above a first predetermined value to interrupt current flow through said circuit breaker; said current limiting device responsive to overload above a second predetermined value to limit current flow therethrough; said second predetermined value corresponding to a severe short condition, and being of a substantially greater magnitude than said first predetermined value; said current limiting device including a first and second terminal; electrical circuit means forming a variable impedance between said first and second terminals; said electrical circuit means operatively including an elongated conductive member, coil wound to form a plurality of turns; first means adapted to progressively move adjacently located ones of said turns between an abutting and non-abutting relationship about their peripheral region; said turns in their abutting relationship effecting a low impedance value between said first and second terminals; said turns in their progressive non-abutting condition progressively increasing the impedance magnitude between said first and second terminals without interrupting the current flow therethrough; said first means constructed to initiate movement of said turns between their abutting and non-abutting relationship responsive to a current presented to said first and second terminals exceeding said second predetermined value, and independent of said circuit breaker operating mechanism.

12. The current protective arrangement of claim 11 wherein said first means including an electromagnetic circuit; said turns being operatively included in said electromagnetic circuit to generate a magnetic flux; adjacent ones of said plurality of turns being progressively moved from said abutting to non-abutting relationship to form a gradually increasing number of series connected turns for generating said magnetic flux; said elongated conductive member formed of a high resistance material; said second impedance magnitude including a substantially greater resistive component than said first impedance magnitude, whereby current limiting is effected between said first and second terminals.

13. The circuit protective arrangement of claim 12 further including a second conductive member series connected with said elongated conductive member between said first and second terminals; said second conductive member positioned about an actuating plunger to generate a magnetic flux through said actuating plunger; said magnetic flux tending to move said actuating plunger in a first direction; said turns operatively connected to said actuating plunger whereby movement of said actuating plunger in said first direction effects said progressive movement of said turns; means biasing said actuating plunger g i st movement in said first direction; the magnetic flux produced by said second conductive member operatively related to said biasing means to initiate movement of said plunger in said first direction responsive to a current flow abovesaid second predetermined value.

14. The circuit protective arrangement of claim 13 whereby said current limiting device includes the series connected arrangement of said first terminal, said actuating plunger, said second conductive member; said elongated conductive member; electromagnetic yoke means; and said second terminal.

15. The circuit protective arrangement of claim 14 wherein said electromagnetic yoke means establishes a flux path including said actuating plunger, and an air gap; said air gap positioned between said actuating plunger and said yoke means; movement of said actuating plunger in said first direction lessening the air gap separation between said actuating plunger and said electromagnetic yoke means.

References Cited by the Examiner UNITED STATES PATENTS 684,165 8/1901 Baker 323-7 2,007,760 7/1935 Hulse 323 66 3,117,257 1/1964 Stone 317-186 3,136,921 9/1964 Dorfman et al. 31711 10 3,192,338 6/1965 Haynes 200-87 JOHN F. COUCH, Primary Examiner.

LLOYD MCCOLLUM, Examiner.

15 W. E. RAY, Assistant Examiner. 

11. A CIRCUIT PROTECTIVE ARRANGEMENT INCLUDING THE SERIES CONNECTIOIN OF A CURRENT INTERRUPTING CIRCUIT BREAKER AND A NON-INTERRUPTING CURRENT LIMITING DEVICE; SAID CURRENT INTERRUPTING CIRCUIT BREAKER INCLUDING AN OPERATING MECHANISM RESPONSIVE TO OVERLOAD ABOVE A FIRST PREDETERMINED VALUE TO INTERRUPT CURRENT FLOW THROUGH SAID CIRCUIT BREAKER; SAID CURRENT LIMITING DEVICE RESPONSIVE TO OVERLOAD ABOVE A SECOND PREDETERMINED VALUE TO LIMIT CURRENT FLOW THERETHROUGH; SAID SECOND PREDETERMINED VALUE CORRESPONDING TO A SEVERE SHORT CONDITION, AND BEING OF A SUBSTANTIALLY GREATER MAGNITUDE THAN SAID FIRST PREDETERMINED VALUE; SAID CURRENT LIMITING DEVICE INCLUDING A FIRST AND SECOND TERMINAL; ELECTRICAL CIRCUIT MEANS FORMING A VARIABLE IMPEDANCE BETWEEN SAID FIRST AND SECOND TERMINALS; SAID ELECTRICAL CIRCUIT MEANS OPERATIVELY INCLUDING AN ELONGATED CONDUCTIVE MEMBER, COIL WOUND TO FORM A PLURALITY OF TURNS; FIRST MEANS ADAPTED TO PROGRESSIVELY MOVE ADJACENTLY LOCATED ONES OF SAID TURNS BETWEEN AN ABUTTING AND NON-ABUTING RELATIONSHIP ABOUT THEIR PERIPHERAL REGION; SAID TURNS IN THEIR ABUTTING RELATIONSHIP EFFECTING A LOW IMPEDANCE VALUE BETWEEN SAID FIRST AND SECOND TERMINALS; SAID TURNS IN THEIR PROGRESSIVE NON-ABUTTING CONDITION PROGRESSIVELY INCREASING THE IMPEDANCE MAGITUDE BETWEEN SAID FIRST AND SECOND TERMINALS WITHOUT INTERRUPTING THE CURRENT FLOW THERETHROUGH; SAID FIRST MEANS CONSTRUCTED TO INITIATE MOVEMENT OF SAID TURNS BETWEEN THEIR ABUTTING AND NON-ABUTTING RELATIONSHIP RESPONSIVE TO A CURRENT PRESENTED TO SAID FIRST AND SECOND TERMINALS EXCEEDING SAID SECOND PREDETERMINED VALUE, AND INDEPENDENT OF SAID CIRCUIT BREAKER OPERATING MECHANISM. 